This invention concerns an apparatus for determining the position of a point on an object or the shape of a portion thereof. Thus it may be employed for producing a plot, contour or measurement of a small object of complicated shape, e.g. a pot shard or a denture cast used in the study or orthodontics, or for determining the co-ordinates of a point or points on an object.
Any form of direct measurement of such an object is necessarily limited, and individual measurements of parts of such an object usually have to be effected independently of each other since a measuring tool capable of reaching all points of such an object is very difficult to design. Detailed measurement of such an object in a defined and constant reference system is usually practical only in some form of indirect measurement where the necessary instrument is not in contact with the object. For example, the object may be photographed from two positions, and the two photographs may be used in a stereo-plotting instrument to provide a plot of the object from which the required measurement or measurements may be made. Such stereo-plotting instruments, however, are very expensive, necessitate considerable operator training, and are subject to the errors arising from photographic distortion.